The present invention relates to a method and apparatus for production line screening and more particularly but not exclusively to screening of semiconductor wafer products at intermediate stages in a multi-tool semiconductor wafer production line.
The semiconductor chip manufacturing process generally involves forming a silicon wafer and then carrying out a sequence of operations that essentially involves addition and selective removal of layers to build the functionality of the chip. The process may typically involve several hundred individual operations including deposition of dielectric and metal layers. Coating of photoresist, photolithography using a mask, etching of layers, ashing etc.
In a manufacturing production line, it is not untypical that something of the order of a thousand wafers may move together through the same sequence of operations at any one time using parallel paths amongst a set of tools. Different tools at different stages take different amounts of time to carry out their processes and thus it is generally found necessary to carry out intelligent routing operations to ensure maximum throughput of wafers. In any kind of routing operation, unless totally straightforward, there is a danger that a batch (or lot) of wafers are misrouted such that operations are carried out in the wrong sequence. Such misrouting leads to scrapping of the entire batch of wafers, generally a very expensive kind of an error just in terms of the batch alone. In addition, entering wafers into the wrong process tools at the wrong time can lead to damage of the process tool, for example due to contamination of the process chamber or the wafer breaking whilst inside the chamber and the like. Damage to the process tool may involve considerable down time, and a repair or replacement cost which is not inconsiderable.
At present the only solutions to routing errors lie in producing more effective and robust routing algorithms. For the vast majority of combinations of steps there is nothing on the wafers themselves that is available for a simple and rapid determination as to whether the wafer approaching a given tool has been through the correct preceding combination of steps.
PCT Patent Application No. WO 0012958 describes a measurement system known as TMS which uses light beams reflected from within layers of a wafer surface to make measurements of the thicknesses of transparent layers and in particular photoresist layers. The measurement is transformed typically into the frequency domain from which it is possible to determine the photoresist layer thickness very accurately. The measurement is quick but typically relates to the thickness or refractive index of a single transparent layer such as a photoresist layer, or to a set of thicknesses of a series of trenches but the system as described does not provide clear overall information that would enable a determination as to where the wafer is in the production line process.
It is an object of the embodiments hereinbelow to provide a solution to the above problem and to allow rapid and practical measurements to be made to a wafer to determine overall what layers it has and thus where it has been in the production process, from which it is possible to determine whether or not it is being correctly routed through the production process.
According to a first aspect of the present invention there is thus provided a production line having a plurality of successive stages for construction of a product comprising at least one layer on a substrate, and routers for transferring partly constructed products between the stages such that each stage receives a respective predefined partly constructed product as its input, the production line comprising:
a predetermined reflected light intensity spectrum for at least one stage representing the respective predefined part construction for the stage,
a reflected light intensity spectrum deriver located at said at least one stage operable to obtain reflected light intensity spectra of incoming partly constructed product, and
a comparator, for comparing said obtained reflected light intensity spectra with said predetermined reflected light intensity spectrum, to determine whether said incoming partly constructed products correspond with said respective predefined part construction for the stage.
The production line preferably further comprises a routing error indicator operatively associated with said comparator for indicating a routing error when said spectra do not match.
The production line preferably further comprises a production interruption mechanism operatively associated with said routing error indicator for interruption of operation of said production line in the event of indication of a routing error.
Preferably, each stage comprises a plurality of production tools operating in parallel.
Preferably, each stage comprises a reflected light intensity spectrum deriver and has a predetermined intensity spectrum.
Preferably, said comparator is further operable to compare said obtained reflected light intensity spectrum with predetermined spectra of at least one other stage to reroute said product to said other stage if said spectra match.
Preferably, said production line is a semiconductor wafer production line for producing a layered semiconductor wafer product.
Preferably, said intensity spectrum deriver comprises
an illuminator for irradiating a part product at at least one point thereof with a multiple wavelength radiation source,
an intensity detector for detecting intensities within reflections of said source from said point,
an analyzer operatively associated with said intensity detector for analyzing said intensities in terms of wavelength and converting said analyzed intensities spectrum into a frequency spectrum thereof, and
a layer property determiner for determining, from said frequency spectrum, layer properties of layers on said part product.
Preferably, said property is one of a group comprising a thickness and a refractive index.
Preferably, said part product includes at least one at least partly transparent layer and said reflections include reflections from an upper and a lower surface of said at least partly transparent layer.
Preferably, said analyzer comprises a Fourier transform calculator for producing said frequency spectrum by Fourier transformation of said analyzed intensity spectrum.
According to a second aspect of the present invention there is provided a tool guard for restricting input to a production tool for carrying out a stage in the production of a layered product, the tool guard comprising:
a predetermined intensity spectrum representing an expected part construction for the stage,
an intensity spectrum deriver located at said tool operable to obtain an intensity spectrum of an incoming partly constructed product, and
a comparator, for comparing said obtained intensity spectrum with said predetermined intensity spectrum, to determine whether said incoming partly constructed product corresponds with said respective predefined part construction for the stage.
The tool guard preferably further comprises a routing error indicator operatively associated with said comparator for indicating a routing error when said spectra do not match.
The tool guard preferably further comprises a production interruption mechanism operatively associated with said routing error indicator for interruption of operation of said tool in the event of indication of a routing error.
Preferably, said tool is a semiconductor wafer production tool for use in a production line producing a layered semiconductor wafer product.
Preferably, said intensity spectrum deriver comprises
an illuminator for irradiating a part product at at least one point thereof with a multiple wavelength radiation source,
an intensity detector for detecting intensities within reflections of said source from said point,
an analyzer operatively associated with said intensity detector for analyzing said intensities in terms of wavelength and converting said analyzed intensities into a frequency spectrum of the intensities, and
a layer property determiner for determining, from said frequency spectrum, layer properties of layers on said part product.
Preferably, said property is one of a group comprising a thickness and a refractive index.
Preferably, said part product includes at least one at least partly transparent layer and said reflections include reflections from an upper and a lower surface of said at least partly transparent layer.
Preferably, said analyzer comprises a Fourier transform calculator for producing said frequency spectrum by Fourier transform of said analyzed intensities.
According to a third aspect of the present invention there is provided a production line router for routing intermediate inputs around a multiple stage production line, the intermediate inputs comprising substrates with at least one superimposed layer, the router comprising:
predetermined intensity spectra for each of a plurality of said stages representing a respective intermediate construction for the stage,
at least one intensity spectrum deriver located within said production line for obtaining intensity spectra of intermediate inputs,
a comparator, for obtaining a closest match between said obtained intensity spectrum and any of said predetermined spectra, said router being operable to route said intermediate input to a stage corresponding to said closest matching spectrum.
Preferably, each stage comprises a plurality of production tools operating in parallel.
Preferably, each stage comprises an intensity spectrum deriver and has a predetermined intensity spectrum.
Preferably, said production line is a semiconductor wafer production line for producing a layered semiconductor wafer product.
Preferably, said intensity spectrum deriver comprises
an illuminator for irradiating a part product at at least one point thereof with a multiple wavelength radiation source,
an intensity detector for detecting intensities within reflections of said source from said point,
an analyzer operatively associated with said intensity detector for analyzing said intensities in terms of wavelength and converting said analyzed intensities into a frequency spectrum of the intensities spectrum, and
a layer property determiner for determining, from said spectrum, layer properties of layers on said part product.
Preferably, said property is one of a group comprising a thickness and a refractive index.
Preferably, said intermediate input includes at least one at least partly transparent layer and said reflections include reflections from an upper and a lower surface of said at least partly transparent layer.
Preferably, said analyzer comprises a Fourier transform calculator for producing said spectrum by Fourier transform of said analyzed intensities.
According to a fourth aspect of the present invention there is provided a wafer production history determiner for determining the production history of a semiconductor wafer product, the determiner comprising:
a plurality of predetermined intensity spectra for semiconductor wafer products having completed respective stages of a multiple stage semiconductor wafer production process,
an intensity spectrum deriver for obtaining an intensity spectrum of an incoming semiconductor wafer product, and
a comparator, for comparing said obtained intensity spectrum with each of said predetermined intensity spectra, to determine a closest match between said obtained spectrum and one of said predetermined spectra, said determiner inferring said production history as including the respective completed stage corresponding to said closest match predetermined spectrum.
According to a fifth aspect of the present invention there is provided the use of a spectrum obtained by reflecting multiple wavelength light from a plurality of points on a layered product, to determine a production history of said layered product.
In a further aspect, in a production line having a plurality of successive stages for construction of a product comprising at least one at least semi-transparent layer on a substrate, and routers for transferring partly constructed product between the stages such that each stage receives a respective predefined partly constructed product as its input, and having a predetermined intensity spectrum associated with at least one stage representing the respective part construction for the stage, there is provided a method comprising:
obtaining intensity spectra of partly constructed products incoming to said stage, and
comparing said obtained intensity spectra with said predetermined intensity spectrum, and thereby determining whether said incoming partly constructed product corresponds with said respective predefined part construction for the respective stage.
Preferably the method further comprises indicating a routing error when said spectra do not match.
Preferably the method further comprises interrupting operation of said production line in the event of indication of a routing error.
Preferably, each stage comprises a plurality of production tools operating in parallel.
Preferably the method further comprises obtaining intensity spectra for incoming partly constructed products to each stage, each said stage having a predetermined intensity spectrum.
Preferably the method further comprises comparing said obtained intensity spectrum with predetermined spectra of at least one other stage to reroute said product to said other stage if said spectra match.
Preferably, said production line is a semiconductor wafer production line for producing a layered semiconductor wafer product.
Preferably, obtaining said intensity spectrum comprises
irradiating a part product at at least one point thereof with a multiple wavelength radiation source,
detecting intensities within reflections of said source from said point,
analyzing said intensities in terms of wavelength, thereby to produce a spectrum of intensities at respective wavelengths,
converting said spectrum of intensities into a frequency spectrum, and
determining, from said frequency spectrum, layer properties of layers on said part product.
Preferably, said property is one of a group comprising a thickness and a refractive index.
Preferably, said part product includes at least one at least partly transparent layer and said reflections include reflections from an upper and a lower surface of said at least partly transparent layer.
Preferably, said converting comprises producing said spectrum by Fourier transform of said analyzed intensities.